KENGNE, E. Perturbation of a Two-Point Problem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 7, p. 980–984, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4498. Acesso em: 6 dec. 2025.